


NEED FOR PHASE ANGLE MEASUREMENT Phase angle meters are used to verify the correct connection of threephase transformer banks which must be paralleled with an existing electrical bus or high voltage line. The process of making these measurements is known as “phasingout” and is performed before the tiein is made. Phase angle measurement is also employed to analyze the operation of AC synchronous generators and synchronous motors to verify the proper operation of field regulators and synchronizing equipment. The Phase angle measurement is used for verifying the proper installation of medium and highvoltage primary metering equipment and sophisticated protective relays that receive input from Potential and Current Transformers (PTs & CTs). Phase Angle Measurement for Power Factor Determination:
The most important application of the equipment which measures phase angle is the determination of power factor for conducting electrical system load studies and power factor correction studies. The system power factor is equal to the cosine of the phase angle that exists between the system voltage and current. In the ideal AC electrical system the voltage and current are in phase. This condition only occurs on systems where the entire load is resistive, such as electric heat, incandescent lighting, or fluorescent lighting with power factor corrected ballasts. Electrical utilization equipment such as motors and welders has a considerable amount of inductance and the inductive reactance (XL which is measured in International Journal of Emerging trends in Engineering and Development Issue 2, Vol.6 (September 2012) Available online on http://www.rspublication.com/ijeted/ijeted_index.htm ISSN 22496149 Page 475 Measurement of Phase Angle using a PLL ohms) causes the circuit current to lag the applied voltage. The actual amount, or number of degrees of lag, depends on the ratio of the Inductive Reactance (XL) in ohms to the ohmic value of Resistance (R) of the system. Once the system power factor is known, power factor correction, if desired, can be applied to the system using power factor correction capacitors or by using synchronous motors, either of which can supply leading Volt Amperes Reactive (VARs) to the system to compensate for the lagging power factor. Most electric utilities charge a penalty for poor system power factor, so keeping the power factor above the required minimum value will result in a lower utility bill and will also improve the voltage drop on the system. Although both the current and the voltage oscillate sinusoidally in an AC circuit they will not necessarily rise and fall simultaneously with each other in each circuit element or the circuit as a whole. The current and voltage will oscillate with the same frequency but they will (in general) be out of phase with each other,exception being when the circuit is in resonance or if there is only resistor in the circuit. The phase difference between two sinusoidal waveforms that have the same frequency and are free of a dc component can be conveniently described as shown in figure 1. It can be seen that the phase angle can be considered as a measure of the time delay between two periodic signals expressed as a fraction of the wave period. This fraction is normally expressed in units of angle, with a full cycle corresponding to 360°. For example, in figure 1, where the voltage v1 passes through zero oneeighth cycles before a second voltage v2, it leads v2 by (360°/8) or 45°.

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